This invention pertains to a system, method and device for the time controlled transmission of an initiation signal from an initiation source to remote blasting elements without the use of lumped delay units.
Typically, mining operations such as quarry excavation, mineral mining and the like require a minimum time separation of 8 milliseconds between detonation of explosive or blasting charges to meet governmental regulations. Conventional detonating cords transmit an initiation signal at a rate of between 5,000-30,000 feet per second or 1,500-9,000 meter/sec. (m/sec). Such propagation rates would require the use of cord lengths in a range of 152-184 feet to achieve the minimum required time delay interval. Similarly, shock tube, such as that described in U.S. Pat. No. 3,590,739, propagates a signal at approximately 6,500 ft/sec, which would require approximately 53 feet of tube to achieve the 8 millisecond delay. Either of these products could conceivably be used to achieve the desired delay interval, but the quantity of product needed is obviously excessive and uneconomical. Safety Fuse.sup.R, an ordinary combustion product propagates a signal at 0.025 ft/sec and is obviously much too slow to transmit the signal. For this reason various delay devices, such as delay elements in detonators, have been incorporated into blasting systems using detonating cord or shock tube to reduce the cord or tube quantities to more manageable lengths.